Red Lights features Sigourney Weaver as Margaret Matheson, a professional debunker of the paranormal. She’s the polar opposite of Weaver’s Ghostbusters character, who served, nearly 30 years ago, as the shrieking human vessel for the raging spirit of the demigod Zuul. In addition to teaching a class on the business of supernatural scams, Margaret and her partner Tom Buckley (Cillian Murphy) make house calls, largely to scoff at alleged poltergeists and the “psychics” who claim to communicate with them. They believe that there’s a con artist behind all paranormal activity; their business is ripping back the curtain. “I don’t do hocus pocus,” she tells another colleague. “I suggest you don’t either.”

Weaver on a haughty high horse is a fair treat, and it would be tempting to describe this as her meatiest part since riding the haughty high horse in Avatar if Red Lights had a better script or wasn’t, in its second half, bewildering on multiple levels, none of them good. It was written and directed by Rodrigo Cortés, whose last movie, Buried (which he directed but didn’t write)is the story of an American contractor buried alive in Iraq who tries to bargain with kidnappers and arrange for rescue via cell phone while six feet under. Buried ended on a sadistic twist; it worked in a kind of unpleasant way but mostly made you wish you hadn’t sat through the movie. Red Lightsreaches for a The Sixth Sense-style twist and whiffs it completely.

It’s unfortunate because the first 30 minutes of the film, in which Margaret and Tom nab various “psychics” and reveal tricks of the trade (like how to levitate a table during a séance) are fun and engaging. Then along comes a really big fish, famed physic Simon Silver (Robert De Niro) who resurfaces after 30 years and announces a comeback tour. Tom is hot to go after him, but Margaret refuses. Simon went into retirement after his biggest foe croaked in the middle of one of his performances, prompting many to believe he put a hex on the guy.

Simon is blind and soft-spoken but menacing. Picture De Niro’s Meet the Parents character with dark sunglasses; maybe he’s not so much bending spoons with his mind as making them wilt. Simon is a jack of all psychic trades, a little magic, a lot of ESP and some diagnostic and healing abilities. Sometimes he just tells people they’re better, but on one occasion, there he is on stage, digging about with his fingers in the abdomen of sedated man until he pries loose some bit of flesh and holds it up triumphantly. Ta-dah. And you thought David Blaine had it going on.

But Simon’s most impressive power is in his ability to intimidate Margaret. The lady is tough, and if she’s scared, that’s saying something. Her fears may or may not have to do with her adult son, who has apparently been in a coma for decades. At some point in his childhood he just “fell over” and hasn’t been right since. Was Simon to blame? This is where Red Lights really starts to go wrong. It over-explains some details, like the stupidity of everyone who isn’t Margaret, particularly her boss at the university, department head Shackleton (Toby Jones), but then plays coy with other information.

At a certain point the story evolves into a battle of wills between Tom and Simon, and Margaret, now absent from the story, is dearly missed. Murphy is great when he’s playing creepy (think of him in Red Eye or Christopher Nolan’s Batman films) and he can pull off vulnerable (as in 28 Days Later or in the underrated The Wind That Shakes the Barley), but he’s not the classic male lead. Here his face has a strange, stretched look to it. It’s a distraction—particularly when Cortés shoots him in close-up walking down a spooky hallway and while the focus is supposed to be on what’s over his shoulder. But it’s not just his appearance; the character is underwritten and inconsistent. He starts sleeping with one student (Elizabeth Olsen) but there’s no sense of attraction or development of the romance—she’s just suddenly in his bed. He ropes in another to help him with key research, and you wouldn’t trust this kid to park your car, let alone solve the riddle of Simon Silver. These characters appear so randomly that it seems there has to be more to them, maybe lying on an editing room floor.By the time Tom is being beaten to a pulp in an epic, nausea-inducing fight in a bathroom, I didn’t much care what happened to him. As for the big twist, which involves, if I’m correct, a psychic fooling his or herself, it’s nonsense. If only Margaret were there to dismiss it as hocus pocus.

Mary Pols has been reviewing film and occasionally books for TIME since 2009. She has degrees from Duke University, where she studied art history, and the University of California Berkeley’s School of Journalism. She is the author of a memoir about untraditional parenthood. It was made into a short-lived television comedy where everything turned out traditionally.

Accidentally on Purpose: The True Tale of a Happy Single Mother is available for nearly nothing at various online bookstores and from boxes in Pols' barn.